Abrasion of caking

ABSTRACT

In a system for the manufacture of cement having a preheater for preheating raw material fed to a heated rotary kiln, apparatus is disclosed for removing caked raw material from those internal wall surfaces of the preheater which are likely to build up such caked material. Cement clinker particles are fed into the preheater and are caused to impinge upon wall areas which are normally subject to caking. Such impingement is at sufficient velocity to dislodge the caking.

United States Patent 1191 Albertus 1 ABRASION OF CAKING [75] inventor: Gundorph Albertus, Copenhagen- Valby, Denmark [73] Assignee: F. L. Smidth & C0., New York,

[22] Filed: Mar. 17, 1969 [21 Appl. No.: 807,852

[30] Foreign Application Priority Data 7 Mar. 20, 1968 Great Britain 13,455/68 [52'] US. Cl ..51/8 [51] Int. Cl ..B24c 3/32 [58] Field of Search ..5l/8, 317, 318, 319, 51/320, 321,13-15 [56] References Cited UNITED STATES PATENTS 782,608 2/1905 Jackson ..51/8 UX 1,058,298 4/1913 Gregg ..5l/8 UX 1451 Apr. 10, 1973 1,795,348 3/1931 Schmidt ..5 U8 UX 2,627,149 2/1953 MacCracken.... ..5 H3 17 2,665,118 H1954 Broman ....5l/32OX 3,207,494 9/1965 Jager ...263/2l A 3,299,459 l/l967 Mccunc ..5l/8 X Primary Examiner-Donald G. Kelly Att0rneyPennie, Edmonds, Morton, Taylor and Adams [5 7] ABSTRACT In a system for the manufacture of cement having a preheater for preheating raw material fed to a heated rotary kiln, apparatus is disclosed for removing caked raw material from those internal wall surfaces of the preheater which are likely to build up such caked material. Cement clinker particles are fed into the preheater and are caused to impinge upon wall areas which are normally subject to caking. Such impingement is at sufficient velocity to dislodge the caking.

14 Claims, 4 Drawing Figures PATENTED R 1 01975 sum 1 or 2 FIG. I 5 40 INVENTOR GUNDORPH ALBERTUS 5% Wp /7 @0' M ATTORNEYS PATENTEUHRWW I 3,726,045

SHEET 2 [IF 2 FIG. 3

INVENTOR GUNDORPH ALBERTUS 5 ATTORNEYS ABRASION or CAKING BACKGROUND OF THE INVENTION In the cement industry and allied industries granular raw material burnt or sintered in a rotary kiln is commonly preheated before entering the kiln by contact with hot gases in a suspension preheater. This may con sist of a series of cyclones connected to one another and to the kiln by pipes, the material being carried upwards in suspension by the hot gases to each cyclone through a riser pipe and entering the kiln from the last cyclone; or again a suspension preheater may consist of a shaft constructed so that someat least of material introduced into the top of it moves downwards against the rising hot gases as a result of being formed into aggregates or dense clouds by circulating gas currents in the shaft or in chambers or sections into which the shaft is directed.

It is often found that the raw material tends to cake on surfaces inside a suspension preheater, the resultant cakes giving rise to serious difficulty in operation. This occurs in practice when the gases contain alkali vapors and chlorides normally of alkali metals. The objective of this invention is to solve this problem.

SUMMARY OF THE INVENTION Caking is prevented or removed, according to the invention, by abrading the surfaces with solid particles or atomized watereither continuously or intermittently. The abrasion may be effected by bombardment with solid particles, the process then being similar to the removal of oxide from metal surfaces by sand blasting; or by bombardment with water, the process thenbeing similar to the cleaning of stone buildings; or by allowing solid particles to. fall under gravity onto or in contact with the surfaces. In each case there is not only abrasive action, but also some cooling which produces temperature differences in cakes already formed so that internal stresses are set up on these and cause them to break. I

Theabrading material must not, of course, interfere with the burning or other process in the kiln or damage the product. If water is used, it will immediately evaporate in the normal preheater, and thus never enter the kiln. If the abrading material is solid, it may most advantageously be particles of the raw material or of the final product. Thus, in the burning of cement, the abrading material may be cement raw meal which may be in the form of nodules, or cement clinker, which may be crushed to some extent or may constitute a fraction from a sieving process to which the clinker may be subjected. Raw meal as such is rather soft and nodules made of it break easily so clinker is the preferred material because of its greater hardness.

If the surfaces are bombarded, as in sand-blasting, the particles are preferably small, not exceeding 2 mm in size. If the abrasion is effected under the influence of gravity, larger particles, say from 5 to 10 mm in size, should be used, such for example, as nodules of cement raw meal.

Naturally only those surfaces on which there is a tendency for cakes to form are abraded. The invention is primarily concerned with suspension preheaters for cement raw meal, and is particularly applicable, although not limited, to cyclone preheaters. These usually comprise several stages, for example four, and generally there is a tendency to caking only in the hottest stage, e.g. that nearest the kiln, and in the pipes between it and the kiln.

Apparatus for carrying out the method may take various forms. If the abrading material is to bombard the surface, pipes terminating in appropriately directed nozzles may be passed through the walls of the cyclones and pipes. If the abrading material is water, it may be supplied to all these pipes through a single main pipe by a water pump. If the abrading material is a solid, means are preferably provided for introducing it individually into each pipe close to the wall of the cyclone or-pipe. These means may advantageously be a hopper and a dosing valve, which can be operated continuously or intermittently as required.

Alternatively, appropriate openings may be made in the walls of the preheater and be closed by cover plates, which can be removed easily when cakes are to be bombarded. Then a suitable apparatus including a flexible pipe with a nozzle can be brought into position so that the nozzle enters each opening in turn, and the internal surfaces are bombarded with water or solid particles through the nozzle.

If the abrading material is to fall under gravity into a cyclone or down a pipe, there-may be a supply hopper and valve at each of a number of openings around the top of the cyclone, or around the pipe at a point where it is reduced in cross-section so that material introduced vertically through the openings will move down the inner surface of the part of the pipe below. Again, atthe top of a cyclone a ring carrying a hopper and dosing valve mounted above an opening in the ring may be arranged to rotate around the vertical axis of the cyclone so that the abrading material isdischarged from the opening into contact with the surface below throughout the rotation.

Two forms of apparatus according to the invention 'will now be described by way of example with reference to the accompanying diagrammatic drawings in which:

FIG. 1 shows the lowermost stage of a cyclone preheater connected to the upper end of a rotary kiln and provided with means for bombarding various surfaces;

FIG. 2 shows a detail of FIG. 1 on an enlarged scale;

FIG. 3 shows the lowermost cyclone of a cyclone preheater provided with means for feeding abrading material under gravity and FIG. 4 shows the parts indicated at B in FIG. 3 onan v enlarged scale.

FIG. 1 shows the upper end of a rotary kiln 1, the mouth of which is surrounded by a casing 2 which joins a riser pipe 3. The riser pipe 3 opens tangentially into a cyclone 4, from the top of which a central gas pipe 5 leads to the next stage of the preheater. Preheated raw meal separated from gas in a cyclone (not shown) in the next stage flows down a pipe 6 to enter the riser pipe 3 and is entrained by the hot gases coming from the rotary kiln, with the result that the temperature of the meal will rise further. The gases carry the raw meal a device 8 which serves to ensure that raw meal may pass down through the pipe 7, while preventing gas from passing through it. The pipe 7 discharges into an inclined pipe 9 by means of which the preheated raw meal is fed into the rotary kiln 1 through the casing 2. The gases leave the cyclone through the pipe to enter the cyclone in the next stage, entraining further raw meal in their passage.

If the hot kiln gases contain alkali vapors or chlorides, there is a tendency to caking. The reason is that these condense on dust and raw meal particles entrained in the gases, the surfaces of these particles become sticky, and some of them adhere to the inner walls of the riser pipe 3 and the cyclone 4; and the cakes formed on these walls form the seats of new sticky particles, and so on.

One of the devices for counteracting caking is shown in FIG. 2, in which 10 denotes a part of the wall of a riser pipe or a cyclone. A pipe 11 passes through the wall 10 and terminates in a nozzle 12 directed downwardly and inwardly towards the wall. Similar pipes 11 are provided at appropriate-angular spacing, for example 90, around the cyclone or pipe, and are all connected to a circular pipe 13 which surrounds the cyclone or pipe and through which compressed air is fed to the pipes 11. Solid abrading material is fed into each pipe 11 from a hopper 16 (not shown in FIG. 2) under the control of'a valve 15, which may be any suitable kind of dosing valve.

In a cyclone preheater caking is found to occur particularly in the conical part of the lowermost cyclone, in the riser pipe to that cyclone, on the outer wall of the curved part of this riser pipe that leads to the cyclone and on that wall of the casing 2 which is struck by the gases from the kiln. Accordingly circular pipes, each with its radiating pipes 11 and nozzle 12, are provided at 13a around the bottom of the part 4a of the cyclone and at 13b around the bottom of the part 40, the nozzles being downwardly directed so as to bombard the surfaces at the upper ends of the parts 4b and 4d respectively. Circular pipes 13c and 13d are provided around the riser pipe 3, the nozzles on the radiating pipes fed by the pipes 13c and 13d being downwardly directed. To counteract caking on the curved part of the riser pipe, a single, upwardly directed nozzle l2e is provided. Finally a single nozzle 12f is downwardly directed to bombard the wall of the casing 2.

The number of nozzles required at any point depends largely on the tendency to caking. As shown, each of the circular pipes 13a and 13d feeds three nozzles and the circular pipes 13b and 130 each feed four nozzles. To reduce the number of containers 16 two nozzles may have a common container 16. On the other hand, the distance between the container and the nozzle should be short.

The abrading material is entrained in the gases,

' separated from them in the cyclone 4 or in a higher stage and finally fed to the kiln through the pipe 9.

The cyclone shown in FIG. 1 is of somewhat unusual shape, the reason being that this shape enables the nozzles to be mounted particularly conveniently for the purpose of keeping the lower part of the cyclone free from cakes.

FIGS. 3 and 4 show the lowermost cyclone 4 of a cyclone preheater, this cyclone consisting only of an upper cylindrical part 4a and a lower conical part 4b. The cyclone is fed by a riser pipe 3 and the gases are discharged from it through a pipe 5. An annular shoulder 33 exists at the top of the cyclone around the pipe 5, and close to the edge of this an annular depression 21 is formed. At the base of this depression there is I a slot 22 giving access to the interior of the cyclone. This slot extends all the way around along the circumference of the cyclone, interrupted at a few points only by bridges (not shown) ensuring connection between the central part of the cover and its outer edge.

A ring 23 fits loosely into the depression 21 and has a single opening which registers with a pipe 24 carrying a dosing valve 25. The pipe 24 is connected to a container 26 containing nodules of raw meal or particles of clinker. The container 26 is carried by a frame 27 which is supported by and mounted to turn round the pipe 5. This frame includes two rings 28 and 29 which mate with sliding surfaces on the pipe, the ring 28 resting on an annular flange 32 that is rigid with the pipe. A gear rim 30 is fixed to the pipe and is engaged by a pinion 31, which is driven through a reducing gear train 35 by a motor 34 carried by the frame 27. Rotation of the motor thus causes the frame 27 to rotate slowly around the pipe 5, carrying the container 26 with it. In the course of one revolution the pipe 24 passes through the entire slot 22 so that nodules or clinker grains from the container 25 will fall very heavily and closely along the inner wall of the cylindrical part 4a of the cyclone and subsequently trickle down the conical part 4b, with the result that the walls of both parts are kept free from caking. The nodules should be sufficiently large and heavy that they will be little affected by the gas circulating in the cyclone.

it will be understood that the foregoing description relates to specific embodiments of the invention and is merely representative. In order to appreciate fully the spirit and scope of the invention, attention is invited to the appended claims.

I claim:

1. An apparatus comprising a multistage suspension preheater having a final stage for use with a heated rotary kiln wherein a burning process takes place utilizing raw cementitious material to produce a cementitious product, the internal wall areas of the final stage of said preheater being subject to caking thereon of said cementitious material fed to said kiln, means for feeding into the preheater particles of cement clinker having no deleterious effect upon the burning process in said rotary kiln or upon its product, means for causing said particles to impinge upon wall areas of the preheater which are subject to caking at sufficient velocity to dislodge said caking, and exit means for passing said particles and dislodged caking to said kiln together with said cementitious material being fed to said kiln.

2. An apparatus according to claim 1 wherein said preheater has a vertical cylindrical pipe section which is provided with conical lower end section while the upper end of said pipe section is formed as a concentrical pipe section of smaller diameter than that of the first mentioned cylindrical pipe section, the difference in diameter between said upper and lower pipe sections forming an annulus which defines openings for the introduction of particles to impinge against internal wall surfaces of the lower end section.

3. An apparatus according to claim 2, characterized in that said annulus defines a large number of openings uniformly distributed between the two cylindrical pipe sections, each opening communicating at its upper end with a separate feed pipe for particles.

4. An apparatus according to claim 2, characterized in that there is only one opening extending as a circumferential slot near the outer edge of said annulus, said opening being covered by an annular lid rotatable about its vertical axis, said lid having opposite the slot at least one bore to which a feed pipe for particles is connected.

5. An apparatus according to claim 4, characterized in that the means for introducing particles comprises a feed pipe, a hopper equipped with means for introducing particles to each feed pipe, means for maintaining an approximately constant level of particles in said hopper and means for stopping or regulating the flow of particles through the feed pipe.

6. An apparatus according to claim 5, characterized in that the container or hopper is rotatable with the annular lid about the axis of the pipe sections.

7. An apparatus according to claim 1, characterized in that the means for introducing the particles comprises at least one feed pipe, a pressure air pipe opening into said feed pipe said pressure air pipe being provided with a particle dosing device arranged such that the particles are introduced into the said air pressure pipe in suitable amounts per unit of time to be entrained by the air therein.

8. An apparatus according to claim 7, characterized in that the dosing device is fitted with an arrangement for stopping or regulating the flow of particles through the feed pipe.

9. An apparatus according to claim 8, characterized in that pressure air pipe manifold in the form of an annular pipe feeds several feed pipes through branch pipes, each branch pipe being associated with a dosing device for said particles.

10. An apparatus according to claim 8, characterized by the provision of a time-controlled impulse transmitter which is connected to said dosing device to transmit impulses for intermittent operation of the dosing device in such manner that these operate alternately with each other.

11. An apparatus according to claim 5 wherein said means for stopping or regulating the flow of particles through the feed pipe is manually operated.

12. An apparatus according to claim 5 wherein said means for stopping or regulating the flow of particles through the feed pipe is automatically operated.

13. An apparatus according to claim 5 wherein said arrangement for stopping or regulating the flow of par ticles through the feed pipe is manually operated.

14. An apparatus according to Claim 5 wherein said arrangement for stopping or regulating the flow of particles through the feed pipe is automatically operated. 

1. An apparatus comprising a multistage suspension preheater having a final stage for use with a heated rotary kiln wherein a burning process takes place utilizing raw cementitious material to produce a cementitious product, the internal wall areas of the final stage of said preheater being subject to caking thereon of said cementitious material fed to said kiln, means for feeding into the preheater particles of cement clinker having no deleterious effect upon the burning process in said rotary kiln or upon its product, means for causing said particles to impinge upon wall areas of the preheater which are subject to caking at sufficient velocity to dislodge said caking, and exit means for passing said particles and dislodged caking to said kiln together with said cementitious material being fed to said kiln.
 2. An apparatus according to claim 1 wherein said preheater has a vertical cylindrical pipe section which is provided with conical lower end section while the upper end of said pipe section is formed as a concentrical pipe section of smaller diameter than that of the first mentioned cylindrical pipe section, the difference in diameter between said upper and lower pipe sections forming an annulus which defines openings for the introduction of particles to impinge against internal wall surfaces of the lower end section.
 3. An apparatus according to claim 2, characterized in that said annulus defines a large number of openings uniformly distributed between the two cylindrical pipe sections, each opening communicating at its upper end with a separate feed pipe for particles.
 4. An apparatus according to claim 2, characterized in that there is only one opening extending as a circumferential slot near the outer edge of said annulus, said opening being covered by an annular lid rotatable about its vertical axis, said lid having opposite the slot at least one bore to which a feed pipe for particles is connected.
 5. An apparatus according to claim 4, characterized in that the means for introducing particles comprises a feed pipe, a hopper equipped with means for introducing particles to each feed pipe, means for maintaining an approximately constant level of particles in said hopper and means for stopping or regulating the flow of particles through the feed pipe.
 6. An apparatus according to claim 5, characterized in that the container or hopper is rotatable with the annular lid about the axis of the pipe sections.
 7. An apparatus according to claim 1, characterized in that the means for introducing the particles comprises at least one feed pipe, a pressure air pipe opening into said feed pipe said pressure air pipe being provided with a particle dosing device arranged such that the particles are introdUced into the said air pressure pipe in suitable amounts per unit of time to be entrained by the air therein.
 8. An apparatus according to claim 7, characterized in that the dosing device is fitted with an arrangement for stopping or regulating the flow of particles through the feed pipe.
 9. An apparatus according to claim 8, characterized in that pressure air pipe manifold in the form of an annular pipe feeds several feed pipes through branch pipes, each branch pipe being associated with a dosing device for said particles.
 10. An apparatus according to claim 8, characterized by the provision of a time-controlled impulse transmitter which is connected to said dosing device to transmit impulses for intermittent operation of the dosing device in such manner that these operate alternately with each other.
 11. An apparatus according to claim 5 wherein said means for stopping or regulating the flow of particles through the feed pipe is manually operated.
 12. An apparatus according to claim 5 wherein said means for stopping or regulating the flow of particles through the feed pipe is automatically operated.
 13. An apparatus according to claim 5 wherein said arrangement for stopping or regulating the flow of particles through the feed pipe is manually operated.
 14. An apparatus according to Claim 5 wherein said arrangement for stopping or regulating the flow of particles through the feed pipe is automatically operated. 